Plasma enhanced chemical processing reactor

ABSTRACT

A plasma enhance chemical processing reactor and method. The reactor includes a plasma chamber and a source of electromagnetic energy. The plasma chamber is in communication with a process chamber which includes a wager support and a gas manifold. The plasma generated in the plasma chamber extends into the process chamber and interacts with the reactive gases to deposit a layer of material on the wafer. The reactor also includes a vacuum system for exhausting the reactor. The method includes the steps of generating a plasma within the plasma chamber, introducing at least one gaseous chemical into the process chamber proximate to the wafer support and applying r.f. gradient to induce diffusion of the plasma to the area proximate the wafer support.

This is a continuation of application Ser. No. 08/909,580 filed Aug. 12,1997, now U.S. Pat. No. 5,792,272 which is a File Wrapper Continuingapplication of application Ser. No. 08/500,493 filed Jul. 10, 1995, nowabandoned.

BRIEF DESCRIPTION OF THE INVENTION

This invention relates to a reactor and method for processingsemiconductor integrated circuits. More particularly, the inventionrelates to a plasma enhanced reactor and method capable of performingprocessing operations including depositing uniform films or layers onthe surface of integrated circuits by plasma enhanced chemical vapordeposition (PECVD), film etchback, reactor self-clean, and simultaneousetch and deposit operations.

BACKGROUND OF THE INVENTION

The processing of semiconductor wafers and other integrated circuits(IC) includes critical manufacturing steps such as etching wafersurfaces and depositing layers of material on wafer surfaces to formdevice components, interconnecting lines, dielectrics, insulatingbarriers and the like. Various systems have been employed to depositlayers of material and the like on the surface of integrated circuits,and often such layers are formed by chemical vapor deposition (CVD). Aconventional thermal CVD process deposits a stable chemical compound onthe surface of a wafer by thermal reaction of certain gaseous chemicals.Various CVD reactors have been used in the art including low pressureCVD systems and atmospheric pressure CVD systems.

More recently, plasma enhanced (sometimes called plasma assisted) CVDsystems (PECVD) have been developed. PECVD systems generally operate bydisassociation and ionization of gaseous chemicals. The high electrontemperatures associated with the plasma increase the density of thedisassociated species available for deposition on the wafer surface.Accordingly, such systems are able to operate at lower temperatures thanconventional thermal CVD systems. Such lower temperature processes aredesirable and minimize diffusion of shallow junctions andinter-diffusion of metals contained within the integrated circuits.Moreover, PECVD systems are suitable for forming multiple dielectriclayers to be used to isolate stacked device features as device densitiesincrease. When forming such multilayer dielectric layers it is desirableto provide a layer with good gap fill, isolation, stress and stepcoverage properties. These properties become more difficult to attain asdevice dimensions shrink.

In PECVD systems, the reactor is typically operated at low pressuresduring processing of the semiconductors. Such low pressures presentparticular gas flow dynamics considerations that must be addressed. Withlow pressures, the collision rate of the active species is relativelylow and the mean-free path of the species is relatively long.Accordingly, it is desirable to provide a reactor capable of uniform,controlled gas flow within the process chamber, across the wafer, and tothe exhaust, thus providing uniform processing of the wafer. Moreover,other operating pressures may be used for various processes, and thus itis desirable for the reactor to be capable of operating over a largepressure range.

Cleaning of the reactor plays an important role in the effectiveoperation of a system. The highly reactive species deposit on the wallsof the chamber, and the operating components, as well as on the surfaceof the substrate. Such deposits affect the operation of the system, mayaffect the plasma potentials within the system, and are a serious sourceof particulates which may end up contaminating the deposited film.Accordingly it is advantageous to provide a reactor design capable ofself cleaning.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of this invention to provide a reactor for processingsemiconductor wafers and integrated circuits.

More particularly, it is an object of this invention to provide animproved reactor for processing wafers by depositing films or layers onthe surface of such wafers by plasma enhanced chemical vapor deposition(PECVD).

Another object of this invention is to provide a reactor which iscapable of operating over a wide pressure range.

Another object of this invention is to provide a reactor capable ofdepositing desired films and simultaneously etching such films.

Yet another object of the invention is to provide a reactor capable ofself-cleaning.

A related object of this invention is to provide a reactor whichimproves the quality of films deposited on wafers.

These and other objects are achieved by the reactor herein disclosedgenerally comprising a plasma chamber communicating with a processchamber. The plasma chamber includes a first gas injection manifold forreceiving at least a first gas; and a source of electromagnetic energywhich excites the gas to form a plasma. The process chamber includes awafer support for supporting a wafer to be processed, and a second gasmanifold which encircles the wafer support and directs reactive gasestoward the wafer support. The plasma generated in the plasma chamberextends into the process chamber and interacts with the reactive gasesto deposit a layer of material on the wafer. A vacuum systemcommunicates with the process chamber for exhausting the reactor.

The invention also includes a method of operating a reactor having aplasma chamber and a process chamber with a wafer support disposedwithin the process chamber, which includes the steps of: generating aplasma within the plasma chamber, introducing at least one gaseouschemical into the process chamber proximate to the wafer support andapplying r.f. gradient to induce diffusion of the plasma to the areaproximate the wafer support, whereby the plasma and the gaseous chemicalinteract proximate the wafer support to form a layer of material on thesurface of the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention become apparent uponreading of the detailed description of the invention and the appendedclaims provided below, and upon reference to the drawings in which:

FIG. 1 is a partially broken away assembly view of the reactor accordingto one embodiment of the invention.

FIG. 2 is an enlarged partially broken away cross-sectional view of theplasma chamber and process chamber of the reactor as shown in FIG. 1.

FIG. 3a illustrates a cross-sectional view of a first gas injectionmanifold according to one embodiment of the invention.

FIG. 3b is bottom plan view of the first gas injection manifold.

FIG. 3c is an enlarged cross-sectional view of the holes in the manifoldof FIG. 3a.

FIG. 4 represents a front plan view, partially broken away, of oneembodiment of a second gas injection manifold in accordance with theinvention.

FIG. 5a is a top plan view showing the substrate support mounted in thereactor.

FIG. 5b depicts an alternate embodiment of the substrate support,partially broken away, mounted in the reactor in accordance with theinvention.

FIG. 6 is a cross-sectional view of the reactor of the invention andillustrates the flow of gases within the system in response to theon-axis placement of the pump.

FIG. 7 is an enlarged side elevated view showing the substrate support,partially broken away, mounted in the reactor in accordance with theinvention.

FIG. 8 is a simplified block diagram illustrating a PECVD system with aplurality of reactors in accordance with an alternative embodiment ofthe invention.

FIG. 9 illustrates sputter rate as a function of substrate support biaspower.

FIGS. 10a and 10 b are cross-sectional views of surface topography ofsemiconductor wafers processed in the reactor of the invention.

FIG. 11 illustrates the deposition rate per silane flow as a function ofthe applied r.f. bias.

DETAILED DESCRIPTION OF THE INVENTION

A. Overview

Turning to the drawings, wherein like components are designated by likereference numbers in the figures, FIGS. 1 and 2 represent one embodimentof the reactor in accordance with this invention. FIG. 1 illustrates anassembly view of the invention wherein reactor 10 generally comprises aplasma assembly 11 and a process chamber 16. The plasma assembly 11which includes a plasma generating source 12, the interior of suchsource 12 forms a plasma chamber 18, and a first gas injection manifold15 forms the top of the chamber. The first manifold 15 conveys at leastone gaseous chemical to plasma chamber 18. The plasma assembly 11 isoperatively attached to process chamber 16. Process chamber 16 generallyincludes a second gas injection manifold 17, which is mounted to processchamber 16, for receiving at least a second gaseous chemical via gasdelivery lines (not shown). Preferably, the gas injection manifold 17 ismounted near the top of chamber 16 with an outer peripheral surfacebeing mounted along the wall of process chamber 16, thus forming acontinuous ring. Further, positioned within chamber 16 is a horizontalwafer support 20 (often referred to as a “chuck”) for supporting a wafer24. Preferably, wafer support 20 is attached to chamber 16 by arm member21 such that the wafer support 20 is suspended within the processchamber 16. A wafer 24 is placed on the wafer support 20 whereby thesurface of the wafer 24 is facing upwards. The wafer support 20 may bebiased by applying r.f. energy from generator 23 via matching network22.

A vacuum system is provided for exhausting the reactor 10. A vacuum pump26 is operatively coupled to the process chamber 16, by port 25.Preferably, vacuum pump 26 is substantially axially aligned with theprocess chamber 16 (referred to as an “on-axis pump”) which providesimproved flow control of the gases and plasma within the reactor 10. Asdiscussed in detail below, the suspended wafer support 20 and theon-axis pumping form a unique gas distribution system which is designedto provide symmetrical flow of gases within the reactor 10, andparticularly to promote uniform deposition and/or etching across thewafer 24.

The inventive reactor is adapted for performing various processingoperations including deposition, film etchback, reactor self-clean andsimultaneous etch and deposition steps. In an exemplary embodiment ofthe deposition operation, silane and a mixture of oxygen and argon areconveyed into the process chamber 16 via second gas injection manifold17. During the deposition operation, the first gas injection manifoldmay be inoperative, and in this configuration, oxygen and argonmolecules migrate into the plasma chamber 18 from the process chamber 16where they are originally injected, and are ionized in plasma chamber18. Alternatively, the first gas injection manifold 15 may be operativewhereby argon and oxygen are conveyed into the plasma chamber via firstgas manifold 15. Furthermore in yet another embodiment, oxygen and argonare conveyed through both the first gas injection manifold 15 and thesecond gas injection manifold 17.

During a reactor self-clean operation, a chemical such as CF₄, C₂F₄ orNH₃ is injected into the plasma chamber via first gas injection manifold15, whereby the gases are ionized and then flow through the reactor 10to remove unwanted deposits on the surfaces of the chambers 16 and 18and associated components. Alternatively, the cleaning chemicals may beinjected into the reactor via second gas injection manifold 17, orconveyed by both the first gas injection manifold 15 and the second gasinjection manifold 17. Moreover, the reactor is adapted for applicationof an r.f. and dc bias induced at the wafer support for inducing a filmetch-back operation and for simultaneous etch/deposit operation. Thereactor and methods are described in further detail below.

B. Plasma Chamber

The plasma assembly 11 can be appreciated in further detail withreference to FIG. 2. Plasma assembly 11 includes a source ofelectromagnetic energy 12, commonly referred to as a “plasma source” forgenerating a plasma within the plasma chamber 18. Preferably the plasmasource 12 is of the type classified in the art as inductively coupledplasma (ICP). In the preferred embodiment as shown in FIG. 2, the plasmasource 12 is cylindrical and includes a helical coil 13 made of metaland a slotted electrostatic shield 19 made of a nonmagnetic material,said shield 19 being generally disposed within the coil 13. The coil 13and shield 19 are housed within an enclosure having an inner 27 andouter 28 wall. Preferably, the inner wall 27 is made of a low lossinsulating material, such as quartz or ceramic, and the outer wall maybe comprised of a metal. Plasma is generated in the plasma chamber 18formed within the plasma source 12. This preferred embodiment of plasmasource 12 is more fully described in U.S. Pat. No. 5,234,529 which isincorporated herein by reference.

A plurality of longitudinally extending and circumferentially spacedslits 33 are formed in the shield 19. The shield 19 is used to decouplecapacitive electric fields. The shield 19 reduces the capacitivecoupling between the coil 13 and the plasma chamber 18 where the plasmais generated. In one embodiment, the plasma source 12 and shield 19attempts to fully shield all capacitive components. Preferably, theshield is grounded. Capacitively coupled fields couple very efficientlywith the plasma, and produce large and generally uncontrollable r.f.plasma potentials. Such a plasma is referred to as a “hot plasma.” Thehot plasma comprises very high plasma particulate energies, particularlyhigh electron temperatures (T_(c)). The resulting high plasma potentialdamages the reactor by the attack of high energy particles at thechamber walls and other components of the reactor. This reduces the lifeof the reactor and creates metal particulate contamination which oftenends up in the deposited film, thereby destroying the wafer. Moreover,the high plasma potential may adversely affect the wafer beingprocessed. By employing the shield 19, the capacitive coupling isreduced to a desired amount, and by varying the slot openings 33 in theshield 19, the amount of capacitive coupling can be varied dependingupon the application. For example, during a clean operation where thereactor 10 is cleaned to remove unwanted deposition of material on thesurfaces of the reactor 10, greater capacitive coupling may be employedthereby creating a higher energy plasma to promote rapid cleaning.

To generate the plasma, according to one embodiment of the invention, atleast one gas is delivered to the plasma chamber 18 by first gasinjection manifold 15. The r.f. energy 14 is directed into plasma source12 through coils 13 arranged around plasma chamber 18 which excites thegases in the plasma chamber 18 into a plasma state. In a plasma state alarge percentage of the gaseous molecules introduced are dissociated toform reactive species, including ionized atoms. Preferably, an iondensity of greater than 10¹¹ ions/cm³ is achieved, and is referred to asa high density plasma (HDP). It is preferred that the frequency of ther.f. energy be 13.56 MHz, a commercial standard frequency. Generator 14typically operates at a standard 50 ohm impedance, and matching network14 a, well known in the art, allows efficient coupling of the r.f.energy into the plasma source 12. Alternatively, gas is conveyed intothe process chamber 16 via second gas injection manifold 17, whereby thegas migrated into the plasma chamber 18 and is excited into a plasmastate as described directly above.

Referring again to FIG. 2, the first gas manifold 15 is illustrated asassembled on the plasma assembly. Further detail is appreciated withreference to FIG. 3a, which depicts a cross-sectional view of saidmanifold 15. In this embodiment, first gas manifold 15 is substantiallycircular and is attached to the inner periphery surface of the plasmasource assembly 12. The manifold 15 includes a plurality of gas inletpassages 32 a and 32 b formed in the manifold base 30. For delivery ofgaseous chemicals to the manifold 15, gas delivery lines (not shown) areconnected to each of the gas inlet passages vias gas feed connectors 31a and 31 b. In this embodiment two gas inlet passages are shown, howeveradditional gas inlet passages, or only one gas inlet passage may beused.

The gas inlet passages 32 a and 32 b individually lead to concentriccircumferentially extending plenums 34 a and 34 b. The plenums extendthrough the manifold base 30 and are enclosed by plate 37 mounted tomanifold base 30. Disposed within each plenum 34 a and 34 b is aplurality of holes 36, drilled in the cover plate 37 and extending thecircumference of each plenum. In one embodiment, the plurality of holes36 are generally disposed at the bottom of each plenum 34 a and 34 b andextend vertically through the cover plate 37. Alternatively, the holes36 may be drilled at an angle through said cover plate 37. Theconfiguration of the holes 36 are selected to provide optimum gasinjection to plasma chamber 18 and the number, size, shape and spacingof the holes may vary. Moreover, concentric hole arrays may be drilledin cover plate 37 and extending the circumference of each plenum.

FIG. 3b illustrates a bottom plan view of first gas injection manifold15. As shown in the present embodiment, the holes 36 generally formconcentric circles in the bottom of first gas injection manifold 15.Preferably, the plurality of holes associated with the inner plenum 34 bcomprises five, and the plurality of holes associated with the outerplenum 34 a comprises ten. FIG. 3c is an enlarged view showing thepreferred shape of hole 36.

Thus, in the present embodiment, gas delivery lines convey gaseouschemicals to the manifold 15 via two gas feed connectors 31 a and 31 b.Each gas is discretely conveyed through the manifold 15 by passages 32 aand 32 b, to circular plenums 34 a and 34 b, whereby the gases exit themanifold 15 through a plurality of holes 36 associated with each plenum,into the plasma chamber 18.

The first gas manifold 15 employs a cooling system for cooling themanifold 15 during operation of the reactor 10. A cooling medium such aswater is circulated through the manifold 15 to provide substantiallyuniform cooling. Maintaining uniform temperature during operation isimportant, as the reaction taking place at the surface of the wafer 24is temperature dependent. Moreover, failure to maintain constanttemperature may lead to flaking of deposits on the chamber walls andassociated components, thereby creating particulates in the system.

In the present embodiment, the cooling medium is delivered throughcooling feed connector 38 to a plurality of channels 42. The channels 42extend through the manifold and are enclosed by a cover plate 43 mountedto the manifold base 30. The channels 42 extend across the manifold base30 as shown in FIG. 3b. In modifications to the invention, the coolingsystem may be configured differently.

A sight glass 39 is suitably disposed in the center of the gas injectionmanifold 15 for providing an optical interface to view the plasmadischarge. Preferably, the sight glass is circular and is made ofsapphire, which resists attack from the plasma and chemicals.Furthermore, sight glass 39 allows line-of-sight access to the waferplane to allow remote diagnostics to be employed such as a laserinterferometer (visible) to observe film growth, and a laserinterferometer (IR) to observe wafer temperature.

Preferably, the manifold 15 has a substantially smooth, planar surfacefor minimizing the depositing of particulate thereon. In this embodimentthe manifold 15 is made from aluminum and has a near polished surfacefinish.

C. Process Chamber

In order to process semiconductor wafers and other ICs, the reactor 10includes a process chamber 16 which is attached to and communicates withplasma assembly 11. Referring again to FIGS. 1 and 2, the internalstructure of the process chamber 16 is illustrated in further detail.Preferably, the process chamber 16 is cylindrical and is made of amaterial such as aluminum. The process chamber 16 preferably includesmeans for a circulating a cooling medium, such as water, such meansformed within the process chamber 16 walls, or alternatively disposed onthe outside of process chamber 16, in order to maintain the processchamber 16 at a constant temperature. A second gas injection manifold 17is disposed within the process chamber 16 and generally extends alongthe surface of the chamber, forming a ring. Also positioned within theprocess chamber 16 is wafer support 20 which supports a wafer 24 to beprocessed. Preferably the wafer support 20 is substantially aligned withthe axis of the process chamber 16, and thus, second gas manifold 17encircles the wafer support 20. A valve (not shown), such as a gatevalve, is disposed in a side wall of the process chamber 16 to allowaccess to the interior of the chamber 16 for transporting the wafer 24to and from the wafer support 20. Positioned beneath the wafer support20 and substantially axially aligned with the axis of the processchamber 16 is a pump 26 and isolation valve 25.

The second gas injection manifold 17 is shown more particularly in FIG.4. Second gas injection manifold 17 is described in further detail inco-pending application, Ser. No. 08/499,861 Flehr, Hohbach, Test et al.,Docket No. A-62196, which is incorporated by reference herein.Generally, the manifold 17 includes a plenum body 40 mountable to theprocess chamber 16, a replaceable nozzle structure 70 removably mountedto the plenum body 40 and at least one plenum formed for receiving agaseous chemical. The plenum body is formed with at least one conduitwhich is coupled to the plenum for conveying the gaseous chemical to theplenum. The nozzle structure 70 has a plurality of nozzles 44 a and 44 bcoupled to the plenum and configured for injecting the gaseous substancefrom the plenum to the chamber. In the present embodiment, the first gasmanifold 17 has an annular configuration with an outer peripheralsurface being mounted to the process chamber 16 wall; however, otherconfigurations are within the scope of the invention.

As shown in FIG. 4, the preferred embodiment of the manifold 17, theplenum body 40 has two parallel, circumferentially extending channels 46and 48 formed in the plenum body 40. The channels 46 and 48 partiallydefine a pair of plenums for discretely receiving the gaseous chemicalsemployed in the processing of the wafer. Channels 46 and 48 are eachconnected to a gas source 50 and 52 (not shown) through conduits 54 and56 via supply lines 58 and 60(not shown). Supply lines 58 and 60 extendvertically to intersect the conduits 54 and 56, and is referred to as“bottom feed” of the gases. In an alternative embodiment, the supplylines 58 and 60 may be configured to extend horizontally through theprocess chamber 16 wall, as a “side feed.”

Preferably, a baffle 62 formed with a plurality of openings (not shown)is mounted in each channel 46 and 48 as is known in the art. Baffles 62interrupt the flow of gas from the conduits 54 and 56 to the nozzles 44a and 44 b adjacent the nozzles to diffuse the gas and more uniformlydistribute the flow of the gas around the circumference of the plenumbody 40. The configuration of the baffles 62 is selected to provideoptimum distribution of the gases and is subject to considerablevariation. Moreover, the baffles 62 may be omitted if desired.

The nozzle structure 70 is removably mounted to the plenum body 40,covering the channels 46 and 48 enclosing the plenums. The nozzlestructure 70 includes a plurality of first nozzles 44 a substantiallyaligned with the channel 46 and a plurality of second nozzles 44 baligned with the channel 48 for injecting the gaseous substancesretained in the plenums into the process chamber 16. The size, shape,spacing, angle and orientation of the nozzles may vary considerably. Thenozzles 44 a and 44 b are preferably configured to provide the layersformed on the surface of wafer 24 with a substantially flat profile.Plenum body 40 and nozzle structure 70 include mating surfaces 80 and 81which are formed to maximize the surface contact between the plenum body40 and the nozzle structure 70 to couple the nozzle structure to ground.

During operation of the reactor 10, and particularly during PECVDprocessing of the wafer 24, the nozzle structure 70 is exposed to theplasma. The gas injection manifold 17 is preferably grounded unless thenozzle structure 70 is formed of a dielectric material.

Manifold 17 is of particular advantage in high density plasma enhancedCVD processing because of the effects on the gas flow of factors such asthe high density of the plasma, the low pressure of the reactor 10 ofless than 3-4 mTorr, as compared to more than 100 mTorr for conventionalplasma enhanced systems, and the relatively high electron temperatureT_(c). Because of the lower chamber pressure, the mean free path islarge and causes quick dispersion of the gaseous chemical away from theinjection point (i.e. the outlet of second gas injection manifold 17),thus the close proximity of the manifold 17 to the surface of the wafer24 allows the efficient use of chemicals and promotes a uniform gasdistribution across the wafer plane.

As mentioned above, for securing the wafer 24 during processing, a wafersupport 20 is provided in process chamber 16. The wafer support 20 isgenerally described below; however, further detail is provided inco-pending application, Ser. No. 08/500,480, Flehr, Hohbach, Test etal., Docket No. A-62195 which incorporated by reference herein.Referring to FIGS. 2, 5 b and 7, the wafer support 20 generally includesa support body 50 having a support surface 52 for retaining a wafer 24,a voltage source 74 coupled to the support body for electrostaticallycoupling the wafer to the support surface, and a cooling system 78 forcooling the wafer. The cooling system includes a plurality of gasdistribution grooves (not shown) formed in the support surface 52 foruniformly distributing a gaseous substance between the wafer 24 and thesupport surface 52. The cooling system includes a restriction mechanism(not shown) in the conduit between the gas source and the gasdistribution grooves to substantially prevent catastrophic separation ofthe wafer 24 from the support surface 52 in the event a portion of thewafer becomes separated from the support surface 52. At least one armmember 21 extending from the support body 50 is mountable to the processchamber 16 with the support body 50 and the arm member 21 beingseparated from the bottom of the process chamber 16. Referring to FIG.7, in the present embodiment the arm member 21 is mounted to a carriageassembly 86 and 88, which in turn is releasably secured by plate 29 tothe process chamber 16.

The wafer 24 is lowered onto and raised from the support surface 52 by alifting assembly (not shown). The lifting assembly includes a pluralityof lifting pins 84 which extend through apertures formed in the supportsurface 52 and an electrode assembly (not shown). The lifting pins 84are movably between an extended position whereby the pins retain thewafer 24 above the support surface 52, and a retracted position.

The wafer support 20 employs a cooling system for cooling the waferduring processing. A gaseous substance such as helium, argon, oxygen,hydrogen and the like, is distributed between the support surface 52 andthe wafer 24 to provide substantially uniform cooling across the entirewafer 24. Maintaining the entire wafer at a uniform temperature duringprocessing significantly improves the uniformity of the layers formed onthe wafer surface.

In the present embodiment, the wafer support 20 is particularly adaptedfor use with PECVD processing. The electrode assembly (not shown)includes means for applying an r.f. bias to the support body 50.Electrode assembly includes a pair of electrical connectors (not shown)which couple inner and outer electrodes and, respectively, to an r.f.source 23 and a matching network 22. Applying an r.f. bias to thesupport surface 52 increases the floating potential of the plasma in thelocalized area of the support surface 52. The self-bias induced byapplying the r.f. bias to the support surface 52 accelerates ionsdiffusing into the plasma sheath in the region of the wafer support 20and towards the wafer 24. This enhances sputter etching which isdesirable in the formation of void-free layers of material on thesurface of the wafer 24.

The frequency of the r.f. bias applied to the wafer support 20 is withinthe range of 1-60 MHz. Preferably, the r.f. frequency of the plasmasource 12 is different from that of the wafer support 20 to minimizefrequency beating. Preferably, the frequency of r.f. applied to thewafer support 20 is approximately 3.39 MHz, and the plasma source 12operates at approximately 13.56 MHz.

During processing, the wafer 24 is positioned on the support surface 52,and particularly placed on lifter pins 54, by a transport device knownin the art (not shown). DC voltage is applied to the at least oneelectrode of the wafer support 20, to electrostatically attract andsecurely retain the wafer to the support surface 52. After processingthe wafer 24, the electrode is substantially grounded in order tosufficiently deactivate the electrostatic charge for release of thewafer 24 from the support surface 52. Preferably, the support body 50includes two electrodes whereby positive voltage is applied to oneelectrode, and negative voltage is applied to the other electrode. Afterthe wafer 24 is removed from the process chamber 16, preferably thepolarity of the electrodes is reversed for the next wafer.

The unique mounting of the wafer support 20 in the process chamber 16 isof particular advantage in processing the wafer 24 substantially due tothe promotion of symmetrical gas flow. Referring again to FIG. 2, atleast one arm member 21 mounts the wafer support 20 to the processchamber 16 such that the wafer support 20 is suspended with the processchamber 16. Suspending the wafer support 20 such that it is removed fromthe bottom of the process chamber 16, unlike prior art systems, offersimproved flow control during processing and increased flexibility in thedesign of the overall reactor 10. In the preferred embodiment, thevacuum system pump 26 is substantially axially aligned with the processchamber 16, minimizing the footprint of the reactor 10 and improving theeffectiveness of the pump during operation.

Turning to FIGS. 5a and 5 b, two embodiments of the wafer support 20mounted in the process chamber 16 are shown. Preferably, two arm members21 a and 21 b extending toward one wall of the process chamber 16 areemployed as depicted in FIG. 5b; however, it is to be understood thatthe number of arm members 21, and their position where attached to theprocess chamber 16, may vary.

Arm members 21 a and 21 b are each formed with a longitudinallyextending bore 60 as illustrated in FIG. 5b. The bore of one arm member21 a provides a conduit from the support body 50 for the electricalconnectors 62 and 64 which couple the electrodes of the wafer support 20to the voltage source 74. Further, electrical connectors 66 and 68couple the r.f. source 23 to the electrodes. The gas source 76 and thefluid source 78 for the electrodes assembly are connected to the supportbody 50 through conduits 72 and 73, respectively, which extend throughthe bore 60 of arm member 21 b. Alternatively, FIG. 5a illustrates theuse of one arm member 21 mounted to process chamber wall 16 whereby thefluid source 78, gas source 76, dc and r.f. sources 74 and 23 and theirrespective connections extend through the bore of arm member 21 to thewafer support 20.

Operatively attached to the process chamber 16 is a vacuum system forexhausting the reactor 10. Referring again to FIG. 1, the vacuum anopening 27, a pump 26 and preferably a vacuum isolation valve 25positioned beneath wafer support 20 and the bottom of the processchamber 16. Preferably, the pump 26 and valve 25 are mountedsubstantially axially aligned with the process chamber 16. Suchinventive “on-axis” pumping is of particular advantage, and promotessymmetrical flow of gases within the reactor 10. Pump 26 and valve 25preferably are a turbo pump and a gate valve, respectively, as known inthe art.

A particular advantage of the invention is the symmetrical flow of thegases within the reactor provided by the inventive design, and thecorresponding reduction of interference with the symmetry of the pumpflow in the region proximate the wafer 24. Referring to FIG. 6, thesymmetrical flow within the reactor 10 is represented by flow lines.

According to the inventive reactor described herein, the placement ofthe side mounted substrate support 20 and the on-axis pumping form aunique gas distribution system that is designed to provide symmetricalflow of gases within the reactor 10, and particularly to promote uniformdeposition and/or etching across the wafer 24.

FIG. 8 depicts an alternative embodiment of the invention, wherein aplurality of reactors 10 a-d are connected by a common transport module75 known in the art, for processing a plurality of wafers. Each reactor10 a, 10 b, 10 c and 10 d may perform a separate processing step, or thesame processing step may be performed in each reactor.

D. Operation of the Reactor

To promote extension of the plasma into the process chamber 16, theinventive reactor induces a potential gradient causing diffusion of theplasma. Plasma is generated close to coil 13 and will diffuses out inany direction. Referring again to FIG. 3a, first gas injection manifoldhas a surface 41 which acts to reference the plasma to a voltagepotential. To direct the plasma, first gas injection manifold 15preferably is grounded which induces the plasma to generate a slightpositive charge at the surface 41 of the manifold 15 (i.e. the plasmapotential). Alternatively, first gas injection manifold 15 may be heldat some potential, instead of ground. Thus, the plasma is referenced toa particular potential in the localized area of the surface 41. Theplasma extends into the plasma chamber 16, and ambipolar diffusion ofthe plasma will replenish any loss of charged particles in the processchamber 16, providing for a steady supply of charged particles in theregion where chemistry is taking place, i.e. at the wafer support 20.Moreover, the plasma generated is a “cold plasma,” i.e. the plasmapotential is low. Thus the potential at the walls is very low, so theplasma is less likely to erode the walls of the chamber which minimizesmetal contamination. Plasma is cold substantially due to theelectrostatic shield 19 which forces the primary ionization mechanism tobe inductive.

Upon application of r.f. bias, a self bias is induced at the wafersupport 20 and wafer 24. Control of the self bias may be effected byconsidering the ratio of the area of the bias r.f. current return pathand the area of the wafer. In one embodiment during the depositionoperation, the self bias accelerates ions from the plasma sheath in thereactor to the surface of the wafer 24. The ions sputter etch the layerof material as it is deposited thereby enhancing deposition of avoid-free, dense good quality film. The r.f. bias applied to the wafersupport may range from 75 to 400 volts, and preferably is approximately300 volts for an r.f. bias power of 1700 Watts.

It is desirable to choose the bias frequency such that it minimizesinterference with the frequency of the plasma source 12 (i.e.intermodulation), and yet is sufficiently high in frequency as to allowfor the induction of the dc self bias at the wafer and to achieve suchbias without excessive power requirements. Generally, lower frequenciesgenerate larger induced voltages at the cost of ripple on top of theinduced voltage. The sputter etch rate at the wafer 24 surface isproportional to the induced bias. An acceptable compromise if found atfrequencies greater than 2 MHz and less than or equal to 13.56 MHz. Thepreferred embodiment employs a r.f. bias frequency applied to the wafersupport 20 of 3.39 MHz; whose first harmonic coincides with a FederalCommunications Commission (FCC) 6.78 ISM frequency (which stands for theInstruments, Scientific and Medical frequency band), and is sufficientlydifferent from the rf plasma source 12 frequency to preventintermodulation thereby minimizing control system instabilities.

The dependency of the sputter etch rate on the bias frequency isillustrated in FIG. 9. A wafer 24 with a layer of oxide is placed on thewafer support 20. The reactor 10 pressure is approximately 1.8 mTorr,and argon gas at approximately 100 sccm is injected into the processchamber 16. Two different bias frequencies, 3.39 MHz and 13.56 MHz, areapplied, and the sputter etch rate is plotted as a function of biaspower applied to the wafer support 20 for the two frequencies.

Circulating r.f. energy fields are present in the reactor 10, and are ofa particular concern when proximate to the wafer 24 in the processchamber 16. One particular advantage of the invention is the function ofthe second gas injection manifold 17 as a r.f. current return path forthe r.f. currents generated by biasing the wafer support with r.f.energy. A substantial amount of the circulating r.f. currents find areturn path through the manifold 17. Referring again to FIG. 4, thesecond gas injection manifold 17 is well grounded through matingsurfaces 80 and 81 which are preferably plated with a suitable materialsuch as nickel to enhance the metal surface-to-surface contact betweenthe plenum body 40 and the nozzle section 70. The interfacing surfacesof the metal are designed to promote low impedance contact and employs aspecial gasket material such as a spiral shield known in the art. Themanifold 17 is coupled to ground and the mating surfaces 80 and 81provide the return path for the r.f. energy generated when an r.f. biasis applied to the wafer support 20. The r.f. currents travel alongsurfaces, not through the bulk of the metal; accordingly, the gasketmaterial is placed close to the metal interfaces. Moreover, theplacement of manifold 17 within the process chamber 16 is important; themanifold 17 is placed in close proximity to the wafer support 20 ascompared to the proximity of the plasma source 12 and first gasinjection manifold 15 to the wafer support 20. The circulating r.f.currents generally encounter the second gas injection manifold 17 andare removed before encountering the other components. In the event ther.f. currents were to return through the plasma source 12, unlike in thepresent invention, the resonance in the plasma source 12 could beadversely affected. Also, as described above, the frequencies aresufficiently different to prevent such occurrences.

The reactor 10 of the invention is particularly suitable for providingstable, substantially repeatable operation by providing isolation of ther.f. currents and plasma potential of the source 12 and first manifold15, from the wafer support 20. Such isolation allows the plasmapotential at the surface 41 of the first gas manifold 15 to be welldefined and maintained. Without a well defined plasma potential, thesystem may differ from day to day depending upon the amount of plasmacontact with the surface 41 of the first gas manifold 15, causing thesystem to drift and adversely effect the repeatability of the depositionprocess. It is important to note that the mechanical configuration ofthe second gas manifold 17 may vary considerably while achieving thesame r.f. return function as described above, and that all suchmechanical variations are within the scope of the invention.

As mentioned above a particular advantage of the invention is thesymmetrical flow of the gases within the reactor provided by theinventive design and the on-axis pump in particular, which correspondsto a reduction of interference with the symmetry of the pump flow in theregion proximate the wafer 24. Referring again to FIG. 6, thesymmetrical flow within the reactor 10 is represented by flow lines, andshows desirable uniform radial flow at the wafer plane. At low pressuresthe mean free path of the gas is relatively long, providing fewercollisions between molecules. It is desirable for the gas density to behighly uniform in the area proximate to the wafer. This is enhanced bythe reactor by providing equal effective pumping speed around the waferplane at the wafer support 20. Equal effective pumping speed isaccomplished by axially aligning the wafer and the pump with the processchamber, so that the geometric orientation (the spacing between theopening of the vacuum system and the wafer support and the size of theopening) promotes equal-distance flow around the wafer. Thus, the flowof gas is symmetrical across the wafer which enhances uniform processingof the wafer. Moreover, during the reactor self-clean operation, gasesare preferably injected through first gas injection manifold 15 andhaving the pump along the axis of symmetry enhances uniform gas flow,and thus cleaning action, throughout the reactor 10.

The inventive reactor 10 design promotes deposition of uniform films asillustrated by FIGS. 10a and 10 b. A wafer 24 is provided having asubstrate 83 with a plurality of device features 85 a-c formed thereon.The gap spacing between device features 85 a and 85 b is 0.25 microns,and the gap spacing between device features 85 a and 85 c is 0.30microns. The aspect ratio is 2.5:1. An oxide layer 82 is deposited ondevice features 85 and substrate 83 in the reactor of this invention. Asshown the reactor 10 and method successfully deposit void-free layersfilling the 0.25 and 0.30 micron gaps with excellent step coverage.

Referring to FIG. 11, the deposition rate as a function of r.f. biasapplied to the wafer support in the invention is illustrated. Thedeposition rate is normalized and is represented as: the deposition rateper silane flow (in angstroms per minute per sccm) which is then plottedas a function of r.f. bias power (watts) applied to the wafer support.

The foregoing description of specific embodiments of the invention havebeen presented for the purpose of illustration and description. They arenot intended to be exhaustive or to limit the invention to the preciseforms disclosed, and obviously many modifications, embodiments, andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be defined by the Claims appended heretoand their equivalents.

What is claimed:
 1. A plasma chemical processing reactor comprising: aplasma chamber having a gas inlet; a source of electromagnetic energydisposed around the plasma chamber for exciting a gas to form a plasma;a process chamber disposed in communication with the plasma chamber; awafer support for supporting a wafer in coupled relationship to saidplasma, said wafer support being suspended in said process chamber; anannular gas manifold, disposed in said process chamber above said wafersupport and mounted along the periphery of said process chamber, fordirecting gases towards said wafer support, whereby gases interact withthe plasma to process the surface of the wafer supported on said wafersupport; and a vacuum system positioned substantially axially alignedwith said process chamber to provide substantially axial flow of thegases around the surface of the wafer and for removing gases from thebottom of said process chamber in a substantially symmetrical manner. 2.The reactor of claim 1 wherein said source of electromagnetic energycomprises an inductively coupled plasma source.
 3. The reactor of claim1 wherein said source of electromagnetic energy comprises a helicalresonator.
 4. The reactor of claim 1, wherein said wafer support isattached to at least one surface on a sidewall portion of said processchamber, such that said wafer support is suspended within said processchamber.
 5. The reactor of claim 1 wherein said vacuum system comprisesa turbo pump.
 6. The reactor of claim 5 wherein said vacuum systemfurther comprises a vacuum isolation valve disposed between said processchamber and said pump for isolating said process chamber from said pump.7. The reactor of claim 1 wherein said gas manifold includes a pluralityof spaced nozzles for distributing gases proximate to said wafer.
 8. Thereactor of claim 1 wherein said wafer support comprises a support bodyhaving a support surface for retaining said wafer; a voltage sourcecoupled to said support body for electrostatically coupling said waferto said support surface; a cooling system having a plurality of gasdistribution grooves formed in said support surface and configured foruniformly distributing a gaseous substance between said wafer and saidsupport surface; at least one member having two ends, one of said endsattached to said support body and the other said ends attached to asurface of said process chamber.
 9. The reactor of claim 8 wherein saidat least one member is attached to a vertical surface of said processchamber such that said support body is suspended within said processchamber.
 10. The reactor of claim 8 wherein said at least one member ishollow and contains therein at least one conduit for passing coolingmedium to said support body, and at least one conduit for coupling dcenergy to said wafer support.
 11. The reactor of claim 10 wherein saidat least one member further comprises at least one conduit for couplingr.f. energy to said wafer support.
 12. The reactor of claim 1 whereinsaid wafer support is attached to a carriage assembly, and said carriageassembly is attached to said process chamber, such that said wafersupport may be removed from said process chamber.
 13. The reactor ofclaim 1 wherein said source of electromagnetic energy comprises ahelical resonator and a capacitive shield disposed within said helicalresonator.
 14. A plasma CVD system for depositing a void free layer ofmaterial on the surface of a wafer, comprising: a plasma chamber havinga source of electromagnetic energy, said source being an inductivelycoupled plasma source for exciting a gas to form a plasma having an iondensity of equal to or greater than 10¹¹ ions/cm³; a process chambercommunicating with said plasma chamber for receiving reactive gases; asupport, in said processing chamber, for supporting the wafer forinteraction with the reactive gases and the plasma extending into theprocess chamber to form a layer of material on the surface of saidwafer; an annular gas manifold, disposed in said process chamber abovesaid support and mounted along the periphery of said process chamber fordirecting the reactive gases toward said support, whereby the reactivegases interact with the plasma to process the surface of said wafersupported on said support; and a vacuum system, with an opening disposeddirectly beneath said support to promote substantially equal effectivepumping speed at the wafer, and for evacuating said process chamber. 15.The reactor of claim 14 wherein said support is attached to at least onesurface of said process chamber, such that said support is suspendedwithin said process chamber.
 16. The reactor of claim 14 wherein saidsupport comprises: a support body having a support surface for retainingsaid wafer; a voltage source coupled to said support body forelectrostatically coupling said wafer to said support surface; a coolingsystem having a plurality of gas distribution grooves formed in saidsupport surface and configured for uniformly distributing a gaseoussubstance between said wafer and said support surface; and at least onemember having two ends, one of said ends attached to said support bodyand the other said ends attached to a surface of said process chamber.17. The reactor of claim 16 wherein said at least one member is hollowand contains therein at least one conduit for passing cooling medium tosaid support body, and at least one conduit for coupling dc energy tosaid support.
 18. The reactor of claim 16 wherein said at least onemember further comprises at least one conduit for coupling r.f. energyto said support.
 19. The plasma CVD system of claim 14 wherein saidsource includes a helical resonator and a capacitive shield disposedwithin said helical resonator.
 20. A plasma chemical processing reactor,comprising: a cylindrical plasma chamber; a source of electromagneticenergy having a helical resonator and a capacitive shield disposedwithin said helical resonator, for generating a plasma having an iondensity of equal to or greater than 10¹¹ ions/cm³; a cylindrical processchamber communicating with the plasma chamber; a wafer support forsupporting a wafer in coupled relationship to said plasma, said wafersupport being disposed on axis within said process chamber and attachedto at least one vertical surface of said process chamber such that saidwafer support is suspended within said process chamber; a continuousannular gas manifold for distributing at least one gas, said manifolddisposed on axis within said process chamber, above said wafer supportand mounted along the periphery of said process chamber, for directingsaid at least one gas towards said wafer support in such proximity thatthe gas density is substantially uniform at the surface of said wafer,whereby the at least one gas deposits a material on the wafer; and avacuum system communicating with said process chamber, with an openingdisposed directly beneath said wafer support to promote substantiallyequal effective pumping speed at the wafer, and being substantiallyaligned on axis with said process chamber, for providing substantiallyaxial flow of the at least one gas around said wafer and for removingsaid gas from said process chamber in a substantially symmetricalmanner.
 21. The reactor of claim 20 wherein said vacuum system comprisesa turbo pump.
 22. The reactor of claim 21 wherein said vacuum systemfurther comprises a vacuum isolation valve disposed between said processchamber and said pump for isolating said process chamber from said pump.23. The reactor of claim 20 wherein said gas manifold includes aplurality of spaced nozzles for distributing gases proximate to saidwafer.
 24. The reactor of claim 20 wherein said wafer support comprises:a support body having a support surface for retaining said wafer; avoltage source coupled to said support body for electrostaticallycoupling said wafer to said support surface; a cooling system having aplurality of gas distribution grooves formed in said support surface andconfigured for uniformly distributing a gaseous substance between saidwafer and said support surface; and at least one member having two ends,one of said ends attached to said support body and the other said endsattached to a surface of said process chamber.
 25. The reactor of claim24 wherein said at least one member is hollow and contains therein atleast one conduit for passing cooling medium to said support body, andat least one conduit for coupling dc energy to said wafer support. 26.The reactor of claim 24 wherein said at least one member furthercomprises at least one conduit for coupling r.f. energy to said wafersupport.
 27. The reactor of claim 20 wherein said wafer support isattached to a carriage assembly, and said carriage assembly is attachedto said process chamber, such that said wafer support may be removedfrom said process chamber.